1. Field of the Invention
The invention relates to polyamide polymers having hot melt adhesive properties and more particularly relates to polyamide resins prepared by the reaction of diamines with a mixture of dimer acids and a specific class of aliphatic dicarboxylic acids.
2. Brief Description of the Prior Art
The prior art is replete with descriptions of polyamide compositions having hot-melt adhesive properties and the methods of their preparation. Representative of the prior art adhesive compositions are those described in U.S. Pat. Nos. 3,377,303 and 3,444,026. The latter compositions comprise the reaction product of a dimer fatty acid and a wide variety of diamines. Copolymerizing dicarboxylic acids including aliphatic dicarboxylic acids such as adipic, sebacic and azelaic acids, are also taught as components of the adhesive compositions.
Polyamide compositions useful as hot-melt adhesives for adhering vinyl plastics are also disclosed in U.S. Pat. No. 3,847,875. The latter compositions are the reaction product of 1,8- or 1,9-heptadecanedicarboxylic acid and specific heterocyclic diamines such as piperazine. Copolymerizable dicarboxylic acids such as azelaic, sebacic and adipic acids are also disclosed as components of the adhesives.
The hot-melt polyamide compositions of the present invention are advantageous for their adhesive strengths in adhering to vinyl resins such as plasticized poly(vinyl chloride) especially at low melt viscosities. However, the compositions of the invention also have good adhesive strengths to degreased steel, aluminum, wood, and various other plastics such as polyolefins, ABS and polystyrene. Particularly advantageous are the compositions' resistance to moisture and elevated temperatures, maintaining good adhesive strengths at elevated temperatures and after exposure to high humidity and/or high temperature conditions.
The invention embodies the unexpected finding that when a 20- or 18-carbon linear dibasic acid is used as a copolymerizing diacid with a polymeric fatty acid and various diamines to prepare polyamide hot-melt adhesives, resins are obtained which have better tensile strengths at ambient and elevated temperatures and increased moisture resistance than when other copolymerizing diacids are used. It is believed that these property improvements are derived primarily from the increased crystallizability imparted to the polyamides by the long chain, linear 20- or 18-carbon dibasic acid. However, this explanation should in no way be considered as definitive or limiting to the scope of the invention.